I. Field of the Disclosure
The technology of the disclosure relates generally to monitoring circuits for monitoring a power supply to determine if a power supply voltage has drooped, and adaptively changing the performance of a powered circuit powered by the power supply in response to compensate for the voltage droop.
II. Background
Circuits such as central processing units (CPUs) or digital signal processors (DSPs) require power to operate. In this regard, a power supply provides a supply voltage to a powered circuit. During normal operation of a circuit, a power supply may undergo a voltage droop. FIG. 1 is a graph illustrating an example of a power supply voltage droop 100 occurring in a supply voltage 102. As shown in FIG. 1, the power supply voltage droop 100 is a temporary drop or reduction (e.g., 10 nanoseconds (ns)) in the power supply voltage 102 being supplied by a power supply. Such behavior may be associated with a switching power supply. Reasons for the power supply voltage droop 100 may include an abrupt increase in demand in power supply current supplied by the power supply, inducing large current transients in a power delivery system, and/or an operational change to the power supply. The magnitude and duration of a voltage droop of a power supply depends on the interaction of capacitive and inductive parasitics at board, package, and die levels with changes in current demand. Thus, voltage droops affect circuits globally across a die and may occur with frequencies ranging in delay from a few nanoseconds (ns) (i.e., high frequency) to a few microseconds (ms) (i.e., low frequency).
High-frequency voltage droops may result in the largest power supply voltage magnitude change, and thus have a severe impact on powered circuit performance and energy efficiency. For example, a CPU that executes instructions may be a powered circuit that is powered by a high frequency switching power supply. In a CPU, typical current consumption may be on the order of hundreds of milliamps (mA) to one (1) amp (A). If for example, the CPU executes back-to-back complex instructions (e.g., hardware multiplies), current consumption may quickly change at about one (1) amp (A) per nanosecond (ns), thereby causing a power supply voltage droop. As long as the voltage droop does not cause the voltage level provided by the power supply to the CPU to fall below the minimum acceptable operating voltage of the CPU, the CPU continues to function properly.
Thus, to compensate for voltage droop that can occur in a power supply supplying power to the CPU, a voltage operating margin (e.g., a voltage guardband) can be designed into the power supply. The voltage operating margin of a power supply is calculated as the difference between the worst-case supply voltage provided by the power supply during voltage droops and the minimum acceptable operating voltage of a powered circuit. The operating margin of the power supply voltage represents additional voltage that must be supplied to the powered circuit to assure proper circuit operation when power supply voltage droop events occur. However, since voltage droops events do not occur frequently, additional power is provided by the power supply to the powered circuit than what is required for the powered circuit to function properly during non-voltage droop times, thus inefficiently expending additional power.
Alternatively, a powered circuit could be configured to operate at a reduced performance level (e.g., reduce its operating frequency) to reduce its minimum acceptable operating voltage. Thus, when voltage droop occurs in the power supply, the powered circuit is already operating at a performance level that can be maintained at the voltage supplied by the power supply during the voltage droop. However, providing for a powered circuit to operate at a reduced performance level to compensate for infrequent power supply voltage droops may also be undesired.